Condensers that are applied to nuclear power plants, thermal power plants and the like, condense turbine exhaust steam, which has been expanded by a steam turbine, into condensate using cooling water. The condensate is supplied to a steam generator through feed-water heaters. The condensers are maintained under vacuum such that thermal energy of turbine exhaust steam can be collected as much as possible when the turbine exhaust steam is condensed into condensate. A condenser that is maintained under vacuum to condense turbine exhaust steam into condensate usually has a steam turbine on its head side.
As the vacuum of a condenser becomes high, the output of a steam turbine increases to improve plant efficiency, while as the temperature of condensate condensed by a condenser becomes high when the condensate is supplied to feed-water heaters, plant efficiency improves. As a system that is effective in improving plant efficiency, a multistage-pressure condenser (which is also called a multi-pressure condenser) including a plurality of condensers having different internal pressures has conventionally been used. The following are reasons why the multistage-pressure condenser can improve plant efficiency.
1) The average value of turbine exhaust steam pressures in a multi-pressure condenser is smaller than that in a single-pressure condenser including a plurality of condensers having the same pressure.
2) Condensate condensed by a low-pressure condenser and an intermediate-pressure condenser is caused to flow into a high-pressure condenser having a high saturation temperature and reheated. Thus, the high-temperature condensate can be supplied to feed-water heaters, with the result that the bleed amount of a steam turbine decreases and the output thereof increases.
3) A difference between the saturation temperature of each of the condensers and the temperature of the cooling water outlet thereof, namely, a difference in termination temperature can be widened. Accordingly, the cooling area of the condensers can be reduced.
A method of heating condensate of a low-pressure condenser by steam of a high-pressure condenser is disclosed in, for example, Japanese Patent No. 3706571 (referred to as Patent Document 1 hereinafter) and Jpn. Pat. Appln. KOKAI Publication No. 11-173768 (referred to as Patent Document 2 hereinafter).
The condenser of Patent Document 1 has the following feature. A regeneration room of a low-pressure condenser, which is partitioned by a pressure partition of a perforated plate, includes a tray. Condensate that drops into the tray from the pressure partition is heated using steam from a high-pressure condenser, and condensate that overflows into the regeneration room from the tray is circulated, with the result that surface turbulent flow heat transmission occurs on the surface of the condensate.
In Patent Document 1, however, since the tray is provided under the perforated plate, the internal structure of the condensers is complicated and thus a time for manufacturing the condensers is lengthened. Though Patent Document 1 discloses using a circulating-flow forming promotion means for condensing steam into condensate by a low-pressure condenser, it does not disclose a method of bringing steam supplied from a high-pressure condenser and condensate condensed by a low-pressure condenser into effective contact with each other. It is deemed that the steam and the condensate are not mixed together sufficiently.
The condenser of Patent Document 2 has the following feature. A perforated plate is provided on the bottom of the hot well of a low-pressure condenser. A conical obstruction is arranged with its top upward such that condensate drops from the small holes of the perforated plate to the center of the top of the conical obstruction. The condensate contacts the conical obstruction to form a liquid film.
In Patent Document 2, however, since the conical obstruction is provided under the perforated plate, the structure is complicated, which increases an operation step such as welding and lengthens a manufacturing time.
Though a number of proposals are made to reheat the condensate of a multistage-pressure condenser, a structure for the reheating is complicated, and condensate of a low-pressure condenser and steam supplied from a high-pressure condenser are not mixed together effectively.
It is thus desired to propose a multistage-pressure condenser capable of simplifying a structure for reheating of condensate and effectively mixing condensate of a low-pressure condenser and steam supplied from a high-pressure condenser together.